1. Technical Field
This invention relates generally to wireless radio telephones and, more particularly, to radio telephones operative with a private base station and public base stations in a wireless system.
2. Description of the Prior Art
With the growing popularity of mobile stations, which enables users to establish and maintain telephone communications almost anywhere, increased user flexibility in utilization of these mobile stations is desired. One approach to providing the increased user flexibility while also encouraging greater utilization of the mobile stations is by providing low-power private base stations as described in the Telecommunications Industry Association (TIA) Interim Standard (IS)-136, dated Nov. 17, 1995.
This standard defines a cellular radio interface specification and sets forth parameters through which a user may register his or her mobile station with a private base station. Once the user has registered the mobile station with the private base station, all telephone calls for this mobile station, outgoing as well as incoming, are routed through this private base station.
A private base station, which operates in accordance with the TIA IS-136 cellular radio interface specification, shares the same frequency spectrum with large cells in the public cellular system, but operates at a greatly reduced power level. Also, each private base station is connected to the public switched telephone network and has a land-line subscriber telephone number which allows a subscriber in the public cellular system to use his or her mobile station for making or receiving telephone calls through the public switched telephone network or other similar network that offers the local exchange service. One example of a land-line supported private base station is disclosed in copending and commonly assigned U.S. patent application Ser. No. 08/509,403 which was filed on Jul. 31, 1995.
As set forth in the TIA IS-136 cellular radio interface specification, a mobile station is able to originate and receive telephone calls through a private base station so long as the mobile station is registered with the private base station and also remains within the coverage region of this private base station. Thus, if a user of the mobile station, while on a telephone c(all established through the private base station, moves the mobile station out of the coverage region for the private base station, in accordance with the TIA IS-136 cellular radio interface specification, the call is not handed off to the public cellular system. Even though the user is provided with audio tones notifying him or her that the mobile is approaching the outer limit of the private base station's coverage area, if the user takes no corrective measures and goes beyond the outer fringe of this coverage area, the call will be dropped.
The desired hand-off does not occur since the private base stations are not designed as nor meant to be connected as an integral part of the network of the public cellular system. One option that is available to the user of the mobile station is to terminate the call going through the private base station and reestablish contact with the remote party by using the mobile station to place a telephone call through the public cellular system. While this option may have been generally satisfactory in the past, it is now technically feasible and desirable to provide an arrangement for operation of a private base station through which a hand-off to the public cellular system may be achieved automatically as the mobile station is moved beyond the coverage region provided by the private base station.